package com.cy.pj.common.utils;

public class SnowFlakeUtil {

    //起始的时间戳
    private final static long START_STMP = 1480166465631L;

    //每一部分占用的位数
    private final static long SEQUENCE_BIT = 12; //序列号占用的位数
    private final static long MACHINE_BIT = 5;   //机器标识占用的位数
    private final static long DATACENTER_BIT = 5;//数据中心占用的位数

    //每一部分的最大值
    private final static long MAX_DATACENTER_NUM = -1L ^ (-1L << DATACENTER_BIT);
    private final static long MAX_MACHINE_NUM = -1L ^ (-1L << MACHINE_BIT);
    private final static long MAX_SEQUENCE = -1L ^ (-1L << SEQUENCE_BIT);

    //每一部分向左的位移
    private final static long MACHINE_LEFT = SEQUENCE_BIT;
    private final static long DATACENTER_LEFT = SEQUENCE_BIT + MACHINE_BIT;
    private final static long TIMESTMP_LEFT = DATACENTER_LEFT + DATACENTER_BIT;

    private long datacenterId;  //数据中心
    private long machineId;     //机器标识
    private long sequence = 0L; //序列号
    private long lastStmp = -1L;//上一次时间戳

    /**
     * 如果部署到不同机器上面 ,需要修改下两个参数,不然可能重复
     * // 数据中心1
     * SnowFlakeUtil sf1 = new SnowFlakeUtil(0, 0); // 机器1
     * SnowFlakeUtil sf2 = new SnowFlakeUtil(0, 1); // 机器2
     * SnowFlakeUtil sf3 = new SnowFlakeUtil(0, 2); // 机器3
     * SnowFlakeUtil sf4 = new SnowFlakeUtil(0, 3); // 机器4
     * SnowFlakeUtil sf5 = new SnowFlakeUtil(0, 4); // 机器5
     *
     * // 数据中心2
     * SnowFlakeUtil sf6 = new SnowFlakeUtil(1, 0); // 机器1
     * SnowFlakeUtil sf7 = new SnowFlakeUtil(1, 1); // 机器2
     * SnowFlakeUtil sf8 = new SnowFlakeUtil(1, 2); // 机器3
     * SnowFlakeUtil sf9 = new SnowFlakeUtil(1, 3); // 机器4
     * SnowFlakeUtil sf10 = new SnowFlakeUtil(1, 4); // 机器5
     * @param datacenterId
     * @param machineId
     */
    public SnowFlakeUtil(long datacenterId, long machineId) {
        if (datacenterId > MAX_DATACENTER_NUM || datacenterId < 0) {
            throw new IllegalArgumentException("datacenterId can't be greater than MAX_DATACENTER_NUM or less than 0");
        }
        if (machineId > MAX_MACHINE_NUM || machineId < 0) {
            throw new IllegalArgumentException("machineId can't be greater than MAX_MACHINE_NUM or less than 0");
        }
        this.datacenterId = datacenterId;
        this.machineId = machineId;
    }



/**
 * 产生下一个ID
 *
 * @return
 */
public synchronized long nextId() {
    long currStmp = getNewstmp();
    if (currStmp < lastStmp) {
        throw new RuntimeException("Clock moved backwards.  Refusing to generate id");
    }

    if (currStmp == lastStmp) {
        //相同毫秒内，序列号自增
        sequence = (sequence + 1) & MAX_SEQUENCE;
        //同一毫秒的序列数已经达到最大
        if (sequence == 0L) {
            currStmp = getNextMill();
        }
    } else {
        //不同毫秒内，序列号置为0
        sequence = 0L;
    }

    lastStmp = currStmp;

    return (currStmp - START_STMP) << TIMESTMP_LEFT //时间戳部分
            | datacenterId << DATACENTER_LEFT       //数据中心部分
            | machineId << MACHINE_LEFT             //机器标识部分
            | sequence;                             //序列号部分
}

    private long getNextMill() {
        long mill = getNewstmp();
        while (mill <= lastStmp) {
            mill = getNewstmp();
        }
        return mill;
    }

    private long getNewstmp() {
        return System.currentTimeMillis();
    }
}
